The present invention relates to a display panel and a display device to which the display panel is applied. More specifically, it relates to a display panel having a fluorescence layer which is excited by electrons from a vacuum space to emit light, and a display device into which the display panel is incorporated.
Various flat type (flat panel type) displays are being studied as image display devices which are to replace currently main-stream cathode ray tubes (CRT). The flat type displays include a liquid crystal display (LCD), an electroluminescence display device (ELD) and a plasma display panel (PDP). Further, there is also proposed a cold cathode field emission display device, a so-called field emission device (FED), which is capable of emitting electrons into vacuum from a solid without relying on thermal excitation, and it attracts attention from the viewpoint of a brightness on a screen and a low power consumption.
FIG. 24 shows a typical configuration of FED, in which a display panel 500 and a rear panel 400 are placed to be opposed to each other. These panels 400 and 500 are bonded to each other in circumferential end portions through a frame (not shown), so that vacuum space VAC is formed in a closed space between these two panels. The rear panel 400 has cold cathode field emission devices (to be referred to as xe2x80x9cfield emission devicesxe2x80x9d hereinafter) as electron emitting members. In FIG. 24, there is shown a so-called Spindt type field emission device having a conical electron emitting portion 45 as an example of the field emission device. The Spindt type field emission device comprises a cathode electrode 41 formed on a supporting member 40, an insulating interlayer 42 formed on the cathode electrode 41 and the supporting member 40, a gate electrodes 44 formed on the insulating interlayer 42, and the conical electron emitting portion 45 formed in opening portions 43 provided in the gate electrodes 44 and the insulating interlayer 42. Generally, a predetermined number of the electron emitting portions 45 having a predetermined alignment are so arranged as to correspond to one fluorescence layer 51 to be explained later. A relatively negative voltage (video signal) is applied to the electron emitting portion 45 from a cathode electrode driving circuit 46 through the cathode electrode 41, and a relatively positive voltage (scanning signal) is applied to the gate electrode 44 from a gate electrode driving circuit 47. Electrons are emitted from the top of the electron emitting portion 45 depending upon an electric field generated by the application of these voltages. The electron emitting member is not limited to the above Spindt type field emission device. A so-called edge type field emission device is used in some cases, and other types such as a flat type field emission device, a crown type field emission device and the like are also used in some cases. Further, sometimes the above is the other way round, that is, a scanning signal is inputted to the cathode electrode 41, and a video signal is inputted to the gate electrode 44.
The display panel 500 has a plurality of fluorescence layers 51 formed on a transparent substrate 50 composed of glass or the like, and a conductive reflective film 52. The fluorescence layer 51 is formed in the form of a matrix or stripes, and the conductive reflective film 52 is formed on the fluorescence layer 51 and the transparent substrate 50. A positive voltage higher than the positive voltage applied to the gate electrode 44 is applied to the conductive reflective film 52 from an acceleration power source (anode electrode driving circuit) 53, and the conductive reflective film 52 works to direct electrons emitted into the vacuum space VAC from the electron emitting portion 45 toward the fluorescence layer 51. Further, the conductive reflective film 52 has the following functions. It protects fluorescence particles constituting the fluorescence layer 51 from the sputtering by particles such as ions, it reflects light emitted by the fluorescence layer 51 due to electron excitation toward the transparent substrate 50 to improve the brightness of a display screen viewed from outside the transparent substrate 50, and it also prevents an excess charge to stabilize the potential of the display panel 500. That is, the conductive reflective film 52 has both the function of an anode electrode and the function of a member known as a metal-back layer in the field of cathode ray tubes (CRT). The conductive reflective film 52 is generally composed of an aluminum thin film.
FIG. 25A shows a schematic plan view of a display panel in which the fluorescence layers 51R, 51G and 51B are formed in a matrix form, and FIG. 25B shows a schematic partial cross-sectional view taken along an Xxe2x80x94X line in FIG. 25A. A region where the fluorescence layers 51R, 51G and 51B are arranged is an effective region which practically works as a display device, and an anode electrode forming region corresponds nearly to the above effective region. For clarification, the anode electrode forming region is indicated by slanting lines in FIG. 25A. A circumferential region of the effective region is an idle region which supports functions of the effective region such as the housing of peripheral circuits and the mechanical support of a display screen. A lead portion 54 used for connecting the anode electrode to the acceleration power source (see acceleration power source 53 in FIG. 24) which supplies a power, for example of 5 kV is formed on an edge portion of the transparent substrate 50. Between the acceleration power source and the anode electrode is generally provided a resistance member (a resistance value of 100 Mxcexa9 in a shown example) for preventing an over-current and discharging. The resistance member is provided outside the substrate.
The anode electrode in an FED is not so necessarily required to be composed of the conductive reflective film 52 as described above. As is shown in a schematic partial cross-sectional view of FIG. 25C taken along an Xxe2x80x94X line in FIG. 25A, there may be employed a constitution in which a transparent conductive film 55 formed on the transparent substrate 50 has the function of the anode electrode. The region where the conductive reflective film 52 or the transparent conductive film 55 which works as an anode electrode is formed covers nearly the entire area of the effective region on the transparent substrate 50.
FIG. 26A shows a schematic plan view of a display panel in which the fluorescence layers are formed in a stripe form, and FIGS. 26B and 26C show schematic partial cross-sectional views taken along an Xxe2x80x94X line in FIG. 26A. Some members in FIGS. 26A to 26C are the same as those in FIGS. 25A to 25c and indicated by the same reference numerals, and detailed explanations thereof are omitted. FIG. 26B shows a configuration in which the anode electrode is composed of a conductive reflective film 52. FIG. 26C shows a configuration in which the anode electrode is composed of a transparent conductive film 55. The region where the conductive reflective film 52 or the transparent conductive film 55 which works as an anode electrode is formed covers nearly the entire area of the effective region of the display panel.
Meanwhile, an FED which is a flat type display device has a far smaller flying distance of electrons than a cathode ray tube, so that the electron acceleration voltage cannot be so increased as a cathode ray tube. That is, when the electron acceleration voltage is too high in the FED, a spark discharge is liable to take place very easily between the electron emitting portion on the rear panel and the film which works as an anode electrode, which may highly possibly downgrade the image quality to a large extent. In the discharge generating mechanism in a vacuum space, presumably, a small discharge is first triggered by the release of electrons and ions from electron emitting portions under a strong electric field, and the anode electrode is supplied with energy to increase a local temperature of the anode electrode, or an occlusion gas inside the anode electrode is released or an anode-electrode-forming material itself is vaporized, so that a small discharge grows to be a spark discharge. Beside the acceleration power source, energy stored or accumulated in an electrostatic capacitance between the anode electrode and the electron emitting portion or between the anode electrode and the cathode electrode may possibly become an energy source which promotes the growth to a spark discharge. For inhibiting the spark discharge, it is effective to control the emission of electrons and ions which trigger the discharge, while it is required to control the particles extremely strictly therefor. In a general production process of display panels or display devices using the display panels, practicing the above control involves great technical difficulties.
The FED for which a low acceleration voltage of electrons is inevitably selected causes characteristic problems which are not found in a cathode ray tube. In a cathode ray tube in which high-voltage acceleration is carried out, the penetration depth of electrons into a fluorescence layer is large, so that the energy of the electrons is received in a relatively large region inside the fluorescence layer. A relatively large number of fluorescence particles in the above large region can be therefore simultaneously excited to achieve a high brightness. In contrast, in the FED, the penetration depth of electrons into the fluorescence layer is small, so that the energy of electrons can be received only in a narrow region. For attaining a practically satisfactory brightness, it is required to increase the density of electrons emitted from the field emission device (i.e., to increase a current density) or to irradiate the fluorescence layer with the electrons for a longer time period than in the cathode ray tube. When the anode electrode is formed on the fluorescence layer, the number of electrons which can transmit the anode electrode is increased by limiting the thickness of the anode electrode to approximately 0.07 xcexcm, so that the anode electrode cannot be expected to has such an effect that the metal-back layer (generally having a thickness of approximately 0.2 xcexcm) of the cathode ray tube has on preventing an antistatic charge. It can be therefore said that the fluorescence layer of the field emission device is situated in an environment where it easily degraded due to the long time irradiation of electrons and charging. When the fluorescence layer is composed of a sulfide-containing fluorescence particles, the above degradation appears as a phenomenon in which sulfur as a component thereof is dissociated in the form of a simple substance, sulfur monoxide (SO) or sulfur dioxide (SO2), and the sulfide-containing fluorescence layer changes in composition or is physically disintegrated. The above degradation of the fluorescence layer leads to a variance in the color of emitted light or light emission efficiency and contamination of components inside the FED and finally to a decrease in the reliability and lifetime characteristic of the FED.
Further, the conventional FED has another problem that the brightness of a display screen varies depending upon pixels or sub-pixels selected on the rear panel 400 side. FIGS. 27A and 27B show schematic configurations of the real panel 400. In these Figures, for clarification, a cathode electrodes 41 in a non-selected state (to which a voltage of +50 volts is applied from the cathode electrode driving circuit 46) is indicated by a less dense hatching, and a cathode electrodes 41 in a selected state (to which a voltage of 0 volt is applied from the cathode electrode driving circuit 46) is indicated by a dense hatching. A video signal applied to the cathode electrode 41 in a selected state can have a value of from 0 volt (inclusive) to less than +50 volts depending upon tones, while it is assumed to be 0 volt for simplification. A gate electrodes 44 in a non-selected state (to which a voltage of 0 volt is applied from the gate electrode driving circuit 47) is indicated by a blank, and a gate electrodes 44 in a selected state (to which a voltage of +50 volts is applied from the gate electrode driving circuit 47) is indicated by hatching. A portion where projection images of the cathode electrode 41 and the gate electrode 44 overlap (to be referred to as xe2x80x9coverlap regionxe2x80x9d hereinafter) corresponds to one pixel in a monochromatic display device, or to one sub-pixel in a color display device, and generally, a plurality of field emission devices are arranged per overlap region. An overlap region of the selected cathode electrode 41 and the selected gate electrode 44 is a selected pixel (or a selected sub-pixel), and it is shown by a blank circle in Figure. The gate electrodes 44 will be referred to as a first column, . . . , m-th column, . . . from top to bottom, and the cathode electrodes 41 are referred to as a first row, . . . , n-th row, . . . from left to right.
When it is assumed that the gate electrode 44 on the first column and the cathode electrode 41 on the first row are selected as shown in FIG. 27A, electrons are emitted from the field emission devices arranged in the overlap region positioned on the first column and the first row, and the opposing fluorescence layer 51 emits light. In this case, if it is assumed that a current of 1 xcexcA flows from the display panel 500 toward the rear panel 400, a voltage drop of 1 xcexcAxc3x97100 Mxcexa9=0.1 kilovolt occurs. That is, an acceleration voltage of 5xe2x88x920.1=4.9 kilovolts is applied between the rear panel 400 and the display panel 500. When it is assumed that the gate electrode 44 on the 2nd column is selected and, for example, that five cathode electrodes 41 such as those on the 2nd, 6th, 9th, 11th and 14th rows are selected as shown in FIG. 27B, however, a current which flows from the display panel 500 toward the rear panel 400 has a total value of 5 xcexcA, and a voltage drop of 0.5 kilovolt takes place, so that the acceleration voltage between the rear panel 400 and the display panel 500 decreases to 5.0xe2x88x920.5=4.5 kilovolts. This means a decrease in the energy of electrons which are to collide with the fluorescence layer 52 and a subsequent decrease in the brightness of a display screen. That is, the brightness of the display screen varies depending upon the number of the cathode electrodes 41 to be selected per column of the gate electrodes 44.
It is therefore a first object of the present invention to provide a display panel in which the deterioration of its fluorescence layer caused by a charge can be prevented, and a display device having a long lifetime due to the use of the above display panel.
It is a second object of the present invention to provide a display panel in which a spark discharge can be prevented, and a display device having a long lifetime and high reliability due to the use of the above display panel.
Further, it is a third object of the present invention to provide a display device which exhibits a stabilized brightness on a display screen by keeping a voltage drop in a constant range without regard to the number of selected electrodes to which video signals are inputted on the rear panel side.
The display panel according to a first aspect of the present invention for achieving the above first object is a display panel comprising a substrate, a fluorescence layer which is to be caused to emit light by electrons from a vacuum space, and an anode electrode which is to direct the electrons toward the fluorescence layer,
wherein the anode electrode comprises a lower electrode and an upper electrode.
In the display panel according to the first aspect of the present invention, the anode electrode has a two-layered structure comprising a lower electrode and an upper electrode, and charge is removed through both the lower electrode and the upper electrode, so that the deterioration of the fluorescence layer caused by an excess charge can be prevented.
The display device according a first aspect of the present invention for achieving the above first object is a display device comprising the display panel according to the first aspect of the present invention,
wherein the display panel and a rear panel having a plurality of electron emitting members are arranged to be opposed to each other through a vacuum space,
the display panel comprises a substrate, a fluorescence layer which is to be caused to emit light by electrons emitted from the electron emitting members into the vacuum space, and an anode electrode which is to direct the electrons toward the fluorescence layer, and
the anode electrode comprises a lower electrode and an upper electrode.
In the display panel and the display device according to the first aspect of the present invention, structurally, there can be two cases, such as
(i) a case where the lower electrode is formed on the substrate, the fluorescence layer is formed on the lower electrode and the upper electrode is formed on the fluorescence layer, and
(ii) a case where the fluorescence layer is formed on the substrate, the lower electrode is formed on the fluorescence layer and the upper electrode is formed on the lower electrode.
In both the cases (i) and (ii), the fluorescence layer may be composed of monochromatic fluorescence particles, or it may be composed of fluorescence particles of three primary colors. Further, concerning the alignment configuration of the fluorescence layers, the fluorescence layers may be aligned in the form of a dot matrix, or in the form of stripes. In the alignment configurations of a dot matrix and stripes, gaps between adjacent fluorescence layers may be filled with a black-matrix layer for improving a contrast. When the above black-matrix layer is formed in the case (i), the fluorescence layers and the black-matrix layer are formed on the lower electrode, and the upper electrode is formed on the fluorescence layers and the black-matrix layer. When the above black-matrix layer is formed in the case (ii), the fluorescence layers and the black-matrix layer are formed on the substrate, and the lower electrode is formed on the fluorescence layers and the black-matrix layer. In both the cases, the lower electrode and the upper electrode are electrically connected and have potentials at the same level when the display device is operated.
In each of these cases (i) and (ii), it is determined depending upon which material is used for the lower electrode and the upper electrode, a transparent material or a non-transparent material, whether the material constituting the substrate is transparent or non-transparent. As a consequence, it is determined whether the display device is a transmission type or a reflection type when the display panel is incorporated into the display device. The above transmission type refers to a system in which an image is viewed through the substrate of the display panel, and not only the substrate is required to be transparent, but all the layers interposed between the fluorescence layer and the substrate are also required to be transparent. The above reflection type refers to a system in which an image is viewed through the rear panel placed to be opposed to the display panel, and not only all the components of the rear panel present in the effective region are required to be transparent, but all the layers that are nearer to the rear panel side than the fluorescence layer on the display panel side are also required to be transparent.
In view of the above conditions, the case (i) can be further classified into follows. xe2x80x9cTPxe2x80x9d stands for xe2x80x9ctransparentxe2x80x9d, xe2x80x9cN-TPxe2x80x9d stands for xe2x80x9cnon-transparentxe2x80x9d, xe2x80x9cTRxe2x80x9d stands for xe2x80x9ctransmission type display devicexe2x80x9d, and xe2x80x9cRFxe2x80x9d stands for xe2x80x9creflection type display devicexe2x80x9d.
In view of the above conditions, the case (ii) is further classified into follows.
There may be employed any one of a structure in which both the lower electrode and the upper electrode are so formed as to extend on the entire effective region, a structure in which one is divided into a plurality of independent regions and the other is so formed as to extend on the entire effective region, and a structure in which each of the lower electrode and the upper electrode is divided into a plurality of independent regions. Further, when each of the lower electrode and the upper electrode is divided into a plurality of independent regions, the number of the independent regions of one may be the same, or different from, the number of the independent regions of the other. Particularly, when at least the upper electrode is divided into a plurality of independent regions in the case (i), or when each of the lower electrode and the upper electrode is divided into a plurality of independent regions in the case (ii), the electrostatic capacitance between the anode electrode and the cathode electrode can be decreased due to a decrease in the area of the anode electrode, and the spark discharge can be effectively prevented. A plurality of the independent regions are practically preferably correspondent to a predetermined number of the unit fluorescence layers, and this point will be discussed with regard to a second aspect of the present invention.
The display panel according to a second aspect of the present invention for achieving the above second object is a display panel comprising a substrate, a plurality of unit fluorescence layers which are to be caused to emit light by electrons from a vacuum space, an anode electrode which is to direct the electrons toward the unit fluorescence layers, and a power supply line,
wherein the anode electrode comprises a plurality of independent electrodes so formed as to correspond to a predetermined number of the unit fluorescence layers, and
each independent electrode is connected to an anode electrode driving circuit through the power supply line.
The display device according the second aspect of the present invention for achieving the above second object is a display device using the display panel according to the second aspect of the present invention,
wherein the display panel and a rear panel having a plurality of electron emitting members are arranged to be opposed to each other through a vacuum space,
the display device comprises a substrate, a plurality of unit fluorescence layers which are to be caused to emit light by electrons emitted from the electron emitting members into the vacuum space, an anode electrode which is to direct the electrons toward the unit fluorescence layers, and a power supply line,
the anode electrode comprises a plurality of independent electrodes so formed as to correspond to a predetermined number of the unit fluorescence layers, and
each independent electrode is connected to an anode electrode driving circuit through the power supply line.
The display panel and the display device according to the second aspect of the present invention are based on a basic thought that, instead of preventing the trigger to a discharge, an energy to be stored or accumulated, for example, between the anode electrode and the cathode electrode is controlled to be at a level at which it is not promoted to grow to a spark discharge, so that a discharge of a small scale, if any, is not grown to a spark discharge. Since the anode electrode is formed to have a form of divided independent electrodes having a smaller area each, instead of being so formed as to extend on the entire effective region, the electrostatic capacitance, for example, between the anode electrode and the cathode electrode can be decreased, so that a stored or accumulated energy can be decreased.
The above unit fluorescence layer is defined to a fluorescence layer which generates one bright point on the display panel. In the industrial field of display devices such as a color cathode ray tube, etc., a combination of three fluorescence layers such as a red fluorescence layer, a green fluorescence layer and a blue fluorescence layer corresponding to the three primary colors of R (red), G (green) and B (blue) is called xe2x80x9cpixelxe2x80x9d, and it is often used as a technical unit for a screen fineness. However, the unit fluorescence layer in the present invention differs from the above pixel. The above definition applies to display panels according to all the aspects of the present invention excluding the first aspect of the present invention and also applies to display devices according to all the aspects of the present invention excluding the first aspect of the present invention.
The power supply line may comprise a plurality of unit power supply lines and each unit power supply line is connected to each independent electrode. That is, each unit power supply line is so formed as to correspond to each independent electrode. Such a constitution will be referred to as xe2x80x9csecond-A constitutionxe2x80x9d. Each unit power supply line can be connected to the anode electrode driving circuit by extending each unit power supply line on an idle region to a connecting terminal provided, for example, on one portion of a peripheral area of the display panel and by providing a line from the connecting terminal to the anode electrode driving circuit.
Further, a resistance member may be inserted somewhere in, for example, the middle of each unit power supply line. Such a constitution will be referred to as xe2x80x9csecond-B constitutionxe2x80x9d. When a discharge takes place, the supply of energy from the anode electrode driving circuit can be temporarily discontinued by providing the resistance member. In the second-B constitution, for example, a chip resistor may be inserted, or a resistance film may be formed, as a resistance member somewhere in the middle of each unit power supply line on the idle region. The resistance value of the resistance member is set at a value which is small to such an extent that a voltage drop caused by an anode current during general display operation has almost no effect on the display brightness and which is large to such an extent that the supply of an energy to the anode electrode from the anode electrode driving circuit through the unit power supply line can be virtually shut off when a discharge of a small scale takes place. The above basic thought of dividing the anode electrode and using the resistance member applies also to a display panel and a display device according to a third aspect of the present invention which will be discussed later.
The display panel and the display device according to the second aspect of the present invention may have a constitution in which the independent electrodes are so arranged in a matrix form as to correspond to fluorescence layer groups consisting of a predetermined number of the unit fluorescence layers each, the power supply line has a main line and a plurality of branch lines branching from the main line, and all the independent electrodes included in columns or rows of the matrix are connected to the branch lines common to the columns or rows through resistance films. The above constitution will be referred to as xe2x80x9csecond-C constitutionxe2x80x9d hereinafter. The plane form of each independent electrode is not specially limited, while the plane form is preferably such that gaps between adjacent independent electrodes have no irregular sizes, in view of achieving a uniform brightness distribution in the effective region. The number of the branch lines branching from the main line and the branching direction thereof are not specially limited, either. However, the branch lines preferably have lengths which are as uniform as possible and uniform wiring resistances, in view of achieving a uniform brightness distribution in the effective region. Each branch line may further have a plurality of branch lines being branched therefrom.
In the second-C constitution, the number of the unit fluorescence layers constituting the fluorescence layer group corresponding to one independent electrode is not specially limited. From the viewpoint of a pixel unit of a color display device, one fluorescence layer group may contain the unit fluorescence layers to such a number that a plurality of the pixels can be constituted, or one fluorescence layer group may contain three unit fluorescence layers that can constitute one pixel. Further, one fluorescence layer group may contain one unit fluorescence layer. When one fluorescence layer group contains one unit fluorescence layer, there can be provided a constitution in which the electrostatic capacitance can be minimized in the display panel having an effective region of some finite size. In the display panel having the second-C constitution, preferably, the unit fluorescence layers are arranged in the form of a so-called dot matrix. The above description can also apply to a display panel having a third-A constitution according to a third aspect of the present invention.
In the display panel and the display device according to the second aspect of the present invention, the independent electrodes can be so arranged in the form of stripes as to correspond to the fluorescence layer group consisting of a plurality of the unit fluorescence layers. The above constitution will be referred to as xe2x80x9csecond-D constitutionxe2x80x9d hereinafter. The stripes may be extended in a length direction or a width direction when it is assumed that the effective region has a rectangular form. In the second-D constitution, preferably, the unit fluorescence layers are also arranged in the form of stripes. That is, in this constitution, the unit fluorescence layers for red (R) are arranged in one row to form a red fluorescence layer group, the unit fluorescence layers for green (G) are arranged in one row to form a green layer group, and the unit fluorescence layers for blue (B) are arranged in one row to form a blue fluorescence layer group. One independent electrode may correspond to one row of the fluorescence layer groups of one color, may correspond to a combination of three rows of the fluorescence layer groups of three primary colors, or may correspond to a plurality of combinations of three rows of the fluorescence layer groups of three primary colors. The above description can also apply to a display panel having a third-B constitution according to a third aspect of the present invention.
In the display panel and the display device according to the second aspect of the present invention, the independent electrodes and the power supply line can be composed of a common conductive material layer on the substrate. For example, a conductive material layer composed of a conductive material is formed on the substrate, and the conductive material layer is patterned, whereby the independent electrodes and the power supply line can be simultaneously formed. Otherwise, a conductive material is deposited or screen-printed through a mask or a screen having a pattern of the independent electrodes and the power supply line, whereby the independent electrodes and the power supply line can be simultaneously formed on the substrate. In the display panel having the second-C or second-D constitution, the resistance film can be also formed in the same manner as above. That is, a resistance film composed of a resistance material may be formed on the substrate and patterned to form the resistance member, or a resistance material may be deposited or printed through a mask or a screen having a resistance member pattern, to form the resistance film.
Even in a case where neither the resistance member nor the resistance film is formed on the display panel side, the resistance member(s) may be provided in the anode electrode driving circuit, and the power supply line can be connected to such an anode electrode driving circuit. When a discharge of a small scale takes place between the rear panel and the display panel, therefore, the supply of energy from the anode electrode driving circuit to the anode electrodes through the power supply line can be temporarily shut off to prevent the occurrence of a spark discharge.
The above second-A to second-D constitutions are based on the classification made, in a sense, in view of arrangements of the power supply line and the resistance member or the resistance film and of the formation pattern of the independent electrodes. The display panel and the display device according to the second aspect of the present invention can structurally include the following five cases (1) to (5). That is,
(1) a case where the unit fluorescence layers are formed on the substrate and the independent electrodes are formed on the unit fluorescence layers,
(2) a case where the independent electrodes are formed on the substrate and the unit fluorescence layers are formed on the independent electrodes,
(3) a case where each of the independent electrodes comprises a lower electrode and an upper electrode, the lower electrode is formed on the substrate, the unit fluorescence layer is formed on the lower electrode, and the upper electrode is formed on the unit fluorescence layer and the lower electrode,
(4) a case where each of the independent electrodes comprises a lower electrode and an upper electrode, the unit fluorescence layer is formed on the substrate, the lower electrode is formed on the unit fluorescence layer, and the upper electrode is formed on the lower electrodes, and
(5) a case where the independent electrodes are formed on the substrate, the resistance film extends over onto the independent electrode, and the unit fluorescence layer(s) is (are) formed on the resistance film.
In the case (5), further, an adhesive layer may be formed between the resistance film and the independent electrode and/or between the resistance film and the unit fluorescence layer. In the cases (3) and (4) in which the independent electrodes comprise the upper electrodes and the lower electrodes, not only the second object of the present invention but also the first object of the present invention can be achieved.
In each of these cases (1) to (5), it is determined depending upon which material is used for forming the independent electrodes and the resistance member, a transparent material or non-transparent (reflective) material, whether the material constituting the substrate is transparent or non-transparent. As a consequence, it is determined whether the display device is a transmission type or a reflection type when the display panel is incorporated into the display device.
In view of the above conditions, the case (1) can be further classified into follows. Of these, the case (1-1) is the most excellent in the compatibility with an existing production process for the production of a display panel. That is, the independent electrodes and the power supply line can be constituted by utilizing a conventional conductive material layer used as a conductive reflective layer (corresponding to the metal-back layer of a cathode ray tube).
In view of the above conditions, the case (2) can be further classified into follows. Of these cases, the case (2-2) is the most excellent in the compatibility with an existing production process for the production of a display panel. That is, the independent electrodes and the power supply line can be constituted by utilizing a conventional layer used as a transparent conductive layer.
The case (3) can be classified into (i-1) to (i-4) explained in the first aspect of the present nvention. Further, the case (4) can be classified into (ii-1) to (ii-4) explained in the first aspect of the present invention.
In view of the above conditions, the case (5) can be further classified into follows.
When the adhesive layer is formed between the resistance film and the independent electrode and/or between the resistance film and the fluorescence layer, there can be further many cases depending upon whether the adhesive layer is transparent or non-transparent. In these cases, however, the above discussion can apply to whether the display device is a transmission type or a reflection type. That is, when a transmission type display device is constituted, not only the substrate is required to be transparent, but also all the layers present between the fluorescence layer and the substrate are required to be transparent. When a reflection type display device is constituted, all the components for the rear panel present in the effective region are required to be transparent.
The display panel according to a third aspect of the present invention for achieving the above second object is a display panel comprising a substrate, a plurality of unit fluorescence layers which are to be caused to emit light by electrons from a vacuum space, and an anode electrode which is to direct the electrons toward the unit fluorescence layers,
wherein the anode electrode comprises a plurality of independent electrodes so formed as to correspond to a predetermined number of the unit fluorescence layers,
the display panel has a power supply layer formed on the substrate, an insulating layer formed on the power supply layer, the unit fluorescence layers formed on the power supply layer or the insulating layer, the independent electrodes formed on the unit fluorescence layers and the insulating layer, holes formed in the insulating layer, and resistance layers buried in the holes, and
the independent electrode is connected to the power supply layer with the resistance layer.
The display device according to a third aspect of the present invention for achieving the above second object is a display device in which the display panel according to the third aspect of the present invention is used,
wherein the display panel and a rear panel having a plurality of electron emitting members are arranged to be opposed to each other through a vacuum space,
the display panel comprises a substrate, a plurality of unit fluorescence layers which are to be caused to emit light by electrons emitted from the electron emitting members into the vacuum space, and an anode electrode which is to direct the electrons toward the unit fluorescence layers,
the anode electrode comprises a plurality of independent electrodes so formed as to correspond to a predetermined number of the unit fluorescence layers,
the display panel has a power supply layer formed on the substrate, an insulating layer formed on the power supply layer, the unit fluorescence layers formed on the power supply layer or the insulating layer, the independent electrodes formed on the unit fluorescence layers and the insulating layer, holes formed in the insulating layer, and resistance layers buried in the holes, and
the independent electrode is connected to the power supply layer with the resistance layer.
In the display panel and the display device according to the third aspect of the present invention, the power supply means for supplying a positive voltage to the independent electrodes from the anode electrode driving circuit is not a power supply xe2x80x9clinexe2x80x9d but a power supply xe2x80x9clayerxe2x80x9d. In the display panel and the display device according to the third aspect of the present invention, the power supply means and the independent electrodes are three-dimensionally arranged through the insulating layer. Unlike the display panel and the display device according to the second aspect of the present invention, therefore, it is no longer necessary to figure out a layout of the power supply means and the independent electrodes in one plane, and the power supply means can be formed on the entire surface of the effective region. However, the power supply layer can have any predetermined pattern without any problem. In the display panel and the display device according to the third aspect of the present invention, a charge is removed from the unit fluorescence layers through both the power supply layer and the independent electrodes, so that the first object of the present invention can be also achieved.
In the display panel and the display device according to the third aspect of the present invention, when a plurality of the unit fluorescence layers are formed on the power supply layer, the unit fluorescence layers are in contact with both the power supply layer and the independent electrodes and are therefore required to have good insulating properties, while the display panel is advantageously decreased in thickness since the unit fluorescence layers and the insulating layer are formed nearly in the same plane. When a plurality of the unit fluorescence layers are formed on the insulating layer, it is not critical whether or not the unit fluorescence layers have good insulating properties.
In the display panel and the display device according to the third aspect of the present invention, there may be employed a constitution in which the independent electrodes are so arranged in a matrix form as to correspond to fluorescence layer groups consisting of a predetermined number of the unit fluorescence layers. The above constitution will be referred to as xe2x80x9cthird-A constitutionxe2x80x9d hereinafter. The number of the unit fluorescence layers constituting the unit fluorescence layer group corresponding to one independent electrode is not specially limited, and it may be one. In the display panel and the display device according to the third aspect of the present invention, there may be employed a constitution in which the independent electrodes are so arranged in the form of stripes as to correspond to fluorescence layer groups consisting of a plurality of the unit fluorescence layers. The above constitution will be referred to as xe2x80x9cthird-B constitutionxe2x80x9d hereinafter.
In the display panel according to the third aspect of the present invention, it is also determined depending upon which material is used for forming the independent electrodes, a transparent material or non-transparent (reflective) material, whether the material constituting the substrate is transparent or non-transparent. As a consequence, it is determined whether the display device is a transmission type or a reflection type when the display panel is incorporated into the display device. That is, when a plurality of the unit fluorescence layers are formed on the power supply layer, the same discussion as the discussion of the cases (i-1) to (i-4) can be made by replacing the upper electrode in the previous case (i) with the independent electrode and replacing the lower electrode in the previous case (i) with the power supply layer. When a plurality of the unit fluorescence layers are formed on the insulating layer, it is further required to consider whether the insulating layer is transparent or non-transparent. That is, when the independent electrodes are non-transparent, the substrate and all the layers present between the unit fluorescence layers and the substrate are required to be transparent, and a transmission type display panel can be constituted. When the independent electrodes are transparent, transmission type and reflection type display panels can be constituted if all of the substrate, the power supply layer and the insulating layer are transparent, and a reflection type display panel can be constituted if at least one of the above layers is non-transparent.
In the display device according to each of the first to third aspects of the present invention, a cold cathode field emission device (to be referred to as xe2x80x9cfield emission devicexe2x80x9d hereinafter) is preferred as an electron emitting member. The type of the field emission device is not specially limited, and it can be any one of a Spindt type field emission device, an edge type field emission device, a flat type field emission device, a low-profile type field emission device and a crown type field emission device. Generally, the electron emitting member(s) is arranged in a region where each of projection images of a first electrode group extending in one direction in which scanning signals are inputted and a second electrode group extending in the other direction in which video signals are inputted overlaps each other. In the display device according to each of the second and third aspects of the present invention, preferably, the independent electrodes are arranged in the form of stripes and extend in a direction nearly in parallel with the direction of the second electrode group for achieving the third object of the present invention to prevent a variability of brightness in a display screen caused depending upon the number of selected electrodes of the second electrode group. When the first electrode group comprises gate electrodes, the second electrode group comprises cathode electrodes. When the first electrode group comprises cathode electrodes, the second electrode group comprises gate electrodes.
As a field emission device, a device called a surface conductive type electron emission device is also known in addition to the above types and can be applied to the display device according to any one of the first to third aspects of the present invention. The surface conductive type electron emission device has a constitution in which thin layers of tin oxide (SnO2), gold (Au), indium oxide (In2O3)/tin oxide (SnO2) or palladium oxide (PdO) having a very small area are formed on a substrate composed, for example, of glass and in the form of a matrix, each thin layer comprises two thin layer pieces, a column-direction wiring is connected to one thin layer piece and a row-direction wiring is connected to the other thin layer piece. There is provided a gap of several nano meter between one thin layer piece and the other thin layer piece. The thin layer selected with the column-direction wiring and the row-direction wiring emits electrons through the gap. When the first electrode group comprises the column-direction wirings, the second electrode group comprises the row-direction wirings. When the first electrode group comprises the row-direction wirings, the second electrode group comprises the column-direction wirings.
In the display panel and the display device according to all the aspects of the present invention, the substrate can be any substrate so long as the surface thereof comprises an insulation member. The substrate includes a glass substrate, a glass substrate having a surface on which an insulating film is formed, a quartz substrate, a quartz substrate having a surface on which an insulating film is formed and a semiconductor substrate having a surface on which an insulating film is formed. The substrate is not necessarily required to be transparent when it is used for constituting a reflection type display panel and a reflection type display device. Each of the above substrates may be used for constituting a supporting member for the rear panel.
Examples of materials for constituting the independent electrode, the power supply line, the power supply layer, the lower electrode, the upper electrode, the first electrode group and the second electrode group include metals such as tungsten (W), niobium (Nb), tantalum (Ta), molybdenum (Mo), chromium (Cr), aluminum (Al), copper (Cu), gold (Au), silver (Ag), titanium (Ti) and nickel (Ni), alloys or compounds of these metal elements (e.g., nitrides such as TiN and silicides such as WSi2, MoSi2, TiSi2 and TaSi2), conductive metal oxides such as ITO (indium-tin oxide), indium oxide and zinc oxide, and semiconductor such as silicon. When the above members are formed, a thin layer of the above material is formed on a substratum by a known thin film forming method such as a chemical vapor deposition method, a sputtering method, a vapor deposition method, an ion plating method, an electroplating method, an electroless plating method, a screen-printing method, a laser abrasion method or a sol-gel method. When the thin film is formed on the entire surface of a substratum, the thin film is patterned by a known patterning method to form each member. Each member can be formed by a lift-off method by forming a resist pattern on the substratum prior to the formation of the thin film. Further, the patterning after the formation of the layer is not required if the vapor deposition is carried out with a mask having openings corresponding to the form of the independent electrode or the power supply line or screen-printing is carried out through a screen having the above openings.
Typical examples of the material for constituting the resistance film or the resistance layer include carbon-containing materials, semiconductor materials such as amorphous silicon and refractory metal oxides such as tantalum oxide. The resistance film can be formed by the same method as the method of forming the above members such as the independent electrode and the power supply line. The pattern width and thickness of the resistance film are determined such that the resistance value is small to such an extent that a voltage drop caused by an current flowing from the display panel toward the rear panel during general display operation has almost no effect on the display brightness and that the resistance value is large to such an extent that the supply of energy to the anode electrode from the anode electrode driving circuit through the power supply line or the power supply layer can be virtually shut off when a discharge of a small scale takes place. The resistance value can be set between several tens kxcexa9 and several hundreds Mxcexa9. This resistance value can also apply to the resistance member such as a chip resistor. As a typical material for constituting the adhesive layer, titanium (Ti) can be used.
In the display panel and the display device according to the third aspect of the present invention, the material for constituting the insulating layer includes SiO2, SiN, SiON, SOG (spin on glass) and a glass paste cured product. These materials can be used alone or in combination. The insulating layer can be formed by a known method such as a chemical vapor deposition method, an application method, a sputtering method or a screen-printing method. The above materials and the above method can be applied to the formation of the insulating interlayer which is a component of the cold cathode field emission device.